Plain English Meaning
It is the part of the 5P check where the pilot reviews everything they've told the cockpit's computers and automation to do, and confirms it's all set up correctly for the flight ahead.
Full Definition
In the 5P Check used in Single-Pilot Resource Management (SRM), 'the Programming' refers to the setup, configuration, and management of cockpit avionics and automation — including the autopilot, flight management system (FMS), GPS navigator, electronic flight displays, and any installed glass-cockpit equipment. It covers entering routes, setting frequencies, selecting modes, and ensuring the automation is doing what the pilot intends at each phase of flight.